1. Field of the Invention
This invention relates generally to electronic article surveillance (EAS) systems and, more particularly to a system and method for providing synchronized operation in EAS systems.
2. Description of the Related Art
In acoustomagnetic or magnetomechanical electronic article surveillance, or “EAS,” a detection system may excite an EAS tag by transmitting an electromagnetic burst at a resonance frequency of the tag. When the tag is present within the electromagnetic field created by the transmission burst, the tag begins to resonate with an acoustomagnetic or magnetomechanical response frequency that is detectable by a receiver in the detection system. The detection unit may then provide some type of signal, for example, an alarm signal indicating the detection of a response from an EAS tag.
In EAS systems, the transmitter burst signal typically does not end abruptly, but instead decays exponentially because of transmitter circuit resonance. If the transmissions from nearby units are not time synchronized, false detections may occur because units may transmit and receive at the same frequency. These false detections can result in false alarms.
It is known to use a plurality of detection units, for example, a plurality of detection pedestals to monitor a larger area, such as the exit of a retail store. Each of these pedestals typically include multiple antennas that may be controlled from a single multi-channel controller. This controller coordinates and synchronizes the antenna operation of each of the detection pedestals.
It is also known to use separate controllers at each of the detection units. In this configuration, communication between the controllers is provided to coordinate operation of each of the units, including synchronizing the antenna operation. In these multiple controller systems it is known to use wired synchronization wherein a communication signal is transmitted between controllers via one or more wired connections. The installation and connection of wiring between the detection units may be complicated and time consuming. For example, if trenching an existing floor is needed to install the wiring, this process adds time and cost to the installation. Additionally, the likelihood of installation problems increase, for example, because of the complexity of installation or the use of special tooling.
It is also known to provide wireless synchronization to communicate with other controllers associated with other detection units. In these systems, synchronization communications are transmitted outside the normal transmit window. In particular, synchronization signals are transmitted during the receive window, which may corrupt receive signals over large distances. Further, high sensitivity receivers are used to detect the synchronization signals. This high sensitivity may result in controllers at different locations, for example, different exits, detecting synchronization signals intended for controllers in another location. Thus, isolation is a problem that can result in false communications and control problems.